That is a puzzler. In regards to the parents leaving children, similarly my grandfather and sister were often left whilst both mother and father travelled for work. Even when they were in the main 'home' city (Birmingham) we have postcards sent to each other saying Happy Birthday/ Christmas/New Yr so it seems they weren't together at those times either, although postcards were the equivalent of texts, they are for separate addresses. We do know my grandfather was mainly raised by a nanny.
Perhaps your mother/uncle were left behind for work reasons? I know my grandfather rarely spoke of his time as a child, looking back it must have been so hard being separated from family, yet strangley his younger brother appeared to have been 'favourite' as it were to a point as he often travelled with his mother to Germany and attended school there.
Another similarity we have is the 'secret' of a family member. My great grandfather disappears from the family for 20 odd years and only appears when he died in 1942. He was of 'no fixed abode' and no one spoke of him- yet when his wife died in 1946 she was buired with him and the gravestone enscribed 'beloved wife of the above' sadly I don't think I'll ever know why he was 'kicked out' the family, there are rumours, but no one left to confirm or deny them.
I hope you find some answers, but yes it maybe the family couldn't cope wit the early death so rather than dwell or go through the loss, they tried to ignore it.